Ahh the moving away thing - I used to get a crush on anybody as soon as I found out they were moving out of state
And that is a huge workplace, I can see how that situation they are in is not nearly as likely to cause a lot of the normal problems. I would still want to meet her personally before I moved though, just so she saw I was a real person, and couldn't have the illusion of me not existing, but really that is up to your comfort level.
I suppose the only other thing I'd say to think about with the LDR thing - as I'm pretty hardcore when it comes to being practical. Assuming that her moving would be "the end of that" is a dangerous assumption for him to make, as a few months of them hanging out could really be very bonding, and you never know. Would it cause any financial hardship if he wanted to keep dating her, and you became able to see your OSO?
It's rare that I see anybody post about being in a LDR and content about the amount of time they get to see their LD partners. Budgeting money and time to visit or host out of town partners regularly could hamper being able to plan quality time and trips for the two of you. That is one reason why we here have agreed not to even entertain getting to know people who aren't within a reasonable driving distance.
I think I'm wondering if you're going to agree to something that you would normally be firmly against, just in order to improve chances of him being OK with you meeting OSO someday. That is a slippery slope with the potential to cause distance between you and your husband, especially if you do agree for him to have freedoms you don't. It seems like you two have good communication so as long as you're honest with him that you're agreeing to it with the hope you get to see OSO maybe it won't be a problem at all. I wish you good luck in however it works out.